Prostate cancer is the most common cancer among men in the U.S. (apart from non-melanoma skin cancer), and is a leading cause of death. Unfortunately, well-established risk factors for this disease (e.g., age) are not modifiable. In the search for modifiable predictors, calcium intake has been proposed to be a risk factor. A high intake of calcium may increase risk by down-regulating 1,25 hydroxyvitamin D3, a hormone that inhibits prostate cancer cell growth and development. It is important to clarify the relation between calcium intake and risk of prostate cancer because calcium is important in the prevention and treatment of osteoporosis. Epidemiologic data on the association of calcium intake and prostate cancer risk have been inconsistent. Few studies have specifically investigated intake of calcium from dairy products and risk of prostate cancer. The data on calcium supplement use and prostate cancer risk are even sparser. Additionally, little information is available on whether the association of calcium intake and prostate cancer risk is modified by age. This is an important question since older men are at higher risk of osteoporosis. Finally, there is a suggestion that calcium intake may be more strongly related to advanced prostate cancer, but few data are available. We propose to analyze the associations of calcium intake from dairy products and supplements among 11,122 men (mean age, 67 years) who were free of cancer in 1988. Men reported on their diet, including intake of dairy products and calcium supplements, in 1988. Information on the development of nonfatal prostate cancer is available through 1998; fatal prostate cancer, 1995. We propose to collect another 3 years of mortality data through 1998. We anticipate a total of 800 prostate cancers (including 116 fatal cancers) to occur among subjects, providing sufficient statistical power to address the questions of interest. We will examine the associations of calcium intake from dairy products and supplements with risk of all and fatal prostate cancer. A consistent increased risk seen with both calcium from dairy products and calcium supplements lends weight to the hypothesis that it is calcium, rather than other nutrients in the dairy products, that is responsible for the increased risk. We also will examine men aged <65, 65-74, and 75+ years. This large database provides a unique and cost-effective opportunity to answer questions of public health importance.